Ch. 4 Geology

glass= rocks of unordered ions that are ______ in place

"frozen" randomly

xenoliths

an inclusion of unmelted country rock in an igneous pluton

disconcordant tabular pluton

dike

___cooling=growth of a solid mass of tiny intergrown crystals

rapid

gabbro

-basaltic magma that cooled inside the earth and cooled slowly -dark green to black -composed of pyroxene and calcium-rich plagioclase feldspar -makes significant % of oceanic crust

intrusive igneous rocks (plutonic)

-igneous rocks that form at depth -they are course-grained -observed at the surface in locations where uplifting and erosion have stripped away the overlying rocks

aphanitic (fine-grained) texture

-igneous rocks that form at the surface -cooling is relatively rapid

dark (ferromagnesian) silicates

-rich in iron and/or magnesian -low in silica

2 parts to porphyritic texture

1. phenocrysts (the large crystals in the rock) 2. groundmass (the matrix of smaller crystals in the rock) -->makes the rock with porphyritic texture (porphyry)

what are the 2 extreme magma types?

1. basaltic 2. andesitic/granite

2 major groups of silicate minerals

1. dark (ferromagnesian) silicates 2. light (nonferromagnesian) silicates

magma comes from 3 situations

1. increase in temperature 2. decrease in pressure (decompression melting) 3. addition of volatiles

3 distinct parts of magma

1. liquid component 2. solid component 3. gaseous phase

igneous rocks form in 2 basic settings:

1. magma may crystallize at depth 2. lava may solidify at earth's surface

name the 3 tabular plutons

1. silk 2. dike 3. lopolith

2 types of plutons

1. tabular 2. massive

what 3 factors influence the textures of igneous rocks?

1. the rate at which molten rock cools 2. the amount of silica present 3. the amount of dissolved gases in the magma

intermediate (Andesitic) composition

1/2 femags and 1/2 nonfemags -diorite and andesite

igneous rocks can be divided into broad groups according to their proportions of light and dark minerals

Granitic (felsic) vs. Basaltic (mafic) and andesitic is in between

bowen's reaction series

a concept that illustrates the relationship between magma and the minerals crystallizing from it during the formation of igneous rock -he said that if solid components of a magma remain in contact with the melt, they will chemically react and change minerology

laccolith

a massive igneous body intruded between preexisting strata -intrusions in which igneous rock forcibly injected between sedimentary strata-->arch the beds above while leaving those below relatively flat

pluton

a structure that results from the emplacement and crystallization of magma beneath earth's surface -dead magma chamber that is exposed

amount of silica in granitic magma (a) vs. basaltic magma (b)

a) high in silica content -viscous (thick) b) low in silica -more fluid

quartz crystals (a) vs. feldspar crystals (b)

a) roughly spherical in shape -often glassy and clear to light gray in color b) white to gray or salmon pink in color -exhibit rectangular shape

rocks high in silica contain very little ... (a) vs. rocks rocks low in silica contain...(b)

a) very little iron, magnesium and calcium b) contain large amounts of iron, magnesium and calcium

stock

an offshoot of one of the plutons on batholith

andesite

andesitic composition formed if the magma cools rapidly on the surface of the earth -fine grained rock of volcanic origin -exhibits porphyritic texture

diorite

andesitic composition formed if the magma cools slowly -mineral makeup is primarily sodium rich plagioclase feldspar and amphibole with lesser amounts of biotite -contains increased % of dark silicate minerals

once a magma body forms, its composition can change thru the incorporation of foreign material. process in igneous activity of incorporating country rock into a magma body is _____

assimilation

massive pluton

b/cuz of its gooey material buldging out: non-discript shape; hard to characterize what the pluton looks like tend to be andesitic to granitic magmas consist of anderoite and diorite

gabbro, basalt, and scoria are from what crustal magma?

basaltic

oregon and washington= sites of extensive ____ outpourings

basaltic

largest pluton we find in the crust of the earth; found where we have mountain ranges ______

batholith -occur as mammoth linear structures sierra nevada= an example (its a granitic structure that forms much of the sierra nevada in california)

why does magma rise?

because it is less dense than the surronding rock -magma can forcibly make room for itself by pushing aside the overlying rock (shouldering0

palisade sill

biggest sill in the world/most studied resistant to erosion forms an imposing cliff that can be easily seen from the opposite side of Hudson

we can only get _____ from lopoliths

chromite (source of chrome)--we get this when magma cools

pegmatitic texture

coarse-grained igneous rocks (pegmatites) may form under special conditions -rocks are composed of inerlocking crystals -most occur as small masses or thin veins situated around the margins of large intrusive bodies -form abnormally large crystals

cooling fractures= _____

columnar joints

welded tuff

common type of pyroclastic rock -composed of fine fragments of glass that remained hot enough to fuse together upon impact -consists mostly of tiny glass shards -blankets vast portions of once volcanically active areas of the western U.S

igneous rocks are ______ if they form parallel features such as sedimentary strata

concordant

crystallization

cooling reverses the events of melting

light (nonferromagnesian) silicates

contain greater amounts of potassium, sodium, and calcium (rather than iron and magnesium) -richer in silica than dark silicates

vesicular texture

contains many small cavaties called vesicles

periodite

contains mostly olivine and pyroxene-->almost entirely of femags (so its ultramafic) -main constituent of the upper mantle

olivine, pyroxene, amphibole, and biotite mica are all common ____ of earths crust

dark silicate minerals

when confining pressure drops sufficiently, ______ is triggered

decompression melting (melting that occurs as rock ascends due to a drop in confining pressure)

porphyritic texture

different minerals crystallize under different enviornmental conditions (temps and pressures) -->possible for crystals of one mineral to become quite large before the others form resulting rock= large crystals embedded in a matrix of smaller crystals

tabular-shaped intrusive igneous feature that cuts thru surrounding rock

dikes

____ AND ______ are shallow features occurring where the country rocks are sufficiently brittle to fracture

dikes and sills

dike

disconcordant bodies that cut across bedding surfaces or other structures in the country rock -serve as tabular conduits that TRANSPORT magma -they weather more slowly than the surrounding rock -tend to have a wall-like apperance when exposed to erosion

igneous rocks are ______ if they cut across existing structures

discordant

ultra mafic

dry; NO H20 -mantle magma -missing light elements -when it crystalizes it forms olivine rich rock known as periodite

glassy texture

during some volcanic eruptions, molten rock is ejected into the atmosphere where its quenched quickly -obsidian=common type of natural glass

crystal setting

during the crystallization of magma, the earlier formed minerals are denser than the liquid portion and settle to the bottom of the magma chamber -this allows separation of various components during crystallization of magma

what is the most abundant mineral group and makes up at least 40% of most igneous rocks?

feldspar

granitic rocks are referred to as being ________

felsic -indicates that the rock is composed almost entirely of light-colored silicates

pumice

floats in water -consists of alot of gas bubbles/large % of voids -volcanic rock with glassy texture -forms when large amounts of gas escape thru silica-rich lava -often exist in alternating layers with obsidian

tabular pluton

flows in between layers very liquidy shaped like a table; regular shape find basalt and gabbros almost exclusively

columnar joints

form as igneous rock cool and develop shrinkage fractures that produce elongated, pillar-like columns -pattern of cracks that forms during cooling of molten rock to generate columns

igneous rocks

form as molten rock cools and solidifies -formed by the crystallization of magma

magma

formed by melting that occurs at various levels within Earth's crust and upper mantle -it is completely or partly molten rock which on cooling solidifies to form an igneous rock of silicate minerals -once formed, a body rises toward the surface (because it is less dense than the surrounding rocks)

Granite

formed by slow cooling inside the earth -forms large crystals -best known because of its beauty and abundance -slabs commonly used for tombstones and monuments -course grained rock 25% quartz and 65% feldspar

rhyolite

found around a granitic eruption taking place -composed of the light-colred silicates color=buff to pink -fine grained -frequently contains glass fragments and voids (rapid cooling) -deposits= less common and less volumous (in contrast to granite)

volatiles

gaseous component of magma -materials that will vaporize (form a gas) at surface pressure

lopolith

giant sill magma moves up, gets injected along a layer a spreads out-->the entire central portion sags down cools slowly

produced when molten lava cools too rapidly to permit recrystallization

glass -a solid composed of unordered atoms -happens because molten material is quenched quiclly and there isnt enough time for the ions to arrange into ordered crystalline network

obsidian

glass- no atomic stucture; liquid -formed by rapid cooling on surface of the earth -granitic magma -forms when silica rich lava is quenched quickly -the ions are unordered usually black to reddish brown in color but appears nearly transparent

granite, rhyolite, obsidian and pumice form from which crustal magma?

granitic

____ and _____ melts have increased silica content and are more viscous (thick) than basaltic magmas

granitic and andesitic

earliest formed crystals have space to grow and they tend to ...

have better-developed crystal faces than do the later ones that occupy the remaining spaces

when magma rises thru the crust, it forcefully displaces preexisting crustal rocks referred to as a _____rock

host or country

batholith

huge body of magma seems to push away the strata on the sides -form course-grained granite -top is whats petruding from the ground -sometimes make up large linear mountains

pyroclastic (fragmental) texture

igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent volcanic eruption

extrusive igneous rocks (volcanic)

igneous rocks form when lava solidifies -tend to be fine grained or when volcanic debris falls to earth's surface

granitic composition

igneous rocks that have quartz and feldspar as their dominant minerals -most contain 10% dark silicate minerals (usually biotite mica and amphibole) -rich in silica (70%) -major constituents of the oceanic crust *cool rapidly on surface of the earth-form tiny crystals of quartz, orthoclase, and femag *cool slowly inside the earth-forms large crystals

most magma originates where?

in the upper mantle

some magma will not reach the surface and instead it will crystallize or freeze at the depth where it becomes ________

intrusive igneous rock

crystalline solid

ions are arranged in a closely packed regular pattern -exhibit restricted vibration

what happens when rock melts?

it takes up MORE SPACE and becomes LESS DENSE than the surrounding solid rock

massive pluton where the strata is pushed upward->buldging occurs->and when mass solidifies we get granite

laccolith

national monument in wyoming- Devils Tower is the reminant of a ____

laccolith

quartz, muscovite mica, and feldspar are all _____ silicates

light (nonferromagnesian) silicates

concordent tabular pluton that is huge

lopolith

decrease in confining pressure _____ the melting temperature (aspect of decompression melting)

lowers

minerals with the ____ melting temps are 1st to melt

lowest -if melting continues, minerals with increasing melting points begin to melt

when ions vibrate rapidly enough to overcome the force of their chemical bonds ______ occurs

melting -at this stage ions can slide past each other and the orderly crystalline structure disintegrates -it converts a solid (tight, uniformly packed ions) into a liquid (unordered ions moving randomly about)

rocks with basaltic compositions are referred to as

mafic (from magnesium and ferrum) -these rocks are typically darker and denser than granitic rocks

what is the parent material for igneous rocks?

magma

another way composition of magma can be altered: process occurs when one magma body intrudes another having a different composition

magma mixing -once combined, convective flow may stir the 2 magmas and generate a mass having a composition of the 2

lava

magma that reaches the earth's surface -sometimes emitted as fountains that are produced when escaping gasses propel it from a magma chamber -other times, magma=explosively ejected-->producing dramatic steam and ash eruptions

formation of one or more secondary magmas from a single parent magma=_______

magmatic differentiation

magma's liquid portion is called ______

melt

sills

nearly horizontal, concordant bodies that form when magma exploits weaknesses between sedimentary beds or other foliations -STORES magma -may exhibit columnar jointing

granitic magma (rich in silica) solidifies to form __a______ VS. basaltic magma (low in silica) generates fine grained crystalline rocks

obsidian

tuff

one of the most common pyroclastic rocks -composed mainly of tiny, ash size fragments that were later cemented together

incomplete melting of rocks is what?

partial melting -process produces the most magma

intrusive igneous rocks= _______

plutonic rocks (after pluto, the god of the lower world)

basaltic magmas that originate from direct melting of mantle rocks and are not yet evolved are what kind of magmas?

primary/primitive

principle of cross cutting relationships

principle that says a rock or fault is younger than any rock (or fault) thru which it cuts *has to be younger than the material in which it is sitting

fragments may be very fine ash, molten blobs, or large angular blocks torn from the walls of the vent during the eruption is what kind of texture?

pyroclastic (fragmental) texture

____ rocks are made of individual particles/fragments

pyroclastic ocks

volcanic breccia

pyroclastic rock composed mainly of particles larger than ash

basalts

rapid cooling on the surface -very dark green to black -most common extrusive igneous rock (hawaiian islands and iceland)

scoria

reddish bubbly rock formed by rapid cooling on the surface of the earth basaltic composition

yellow stone park is an exception to ____ because the lava flows and thick ash deposits are EXTENSIVE

rhyolite

basaltic composition

rocks that contain substantial dark silicate minerals and calcium-rich plagioclase feldspar (but no quartz) -referred to as mafic -primarily femags: labrodite and gabbro -->dark to black

igneous compositions: composed mainly of

silicate minerals -silicon and oxygen (most abundant constituents) plus Al, Ca, Na, K, Mg, Fe

concordant tabular pluton

sill *in harmony with the grain of the rock *tabular in shape

tabular igneous body that intruded parallel to the layering of preexisting magma

sills

____ cooling = growth of fewer, but larger crystals

slow

earths crust and mantle is composed primarily of liquid or solid?

solid rock

intrusions or plutons

structures that result from the emplacement of magma into preexisting rocks -all form beneath earth's surface

intrusive igneous bodies are classified according to their shape as either _____ or _______ and by their origination with respect to the host rock

tabular (has 2 dimensions that are much longer than the 3rd) or massive (igneous pluton not tabular in shape)

geothermal gradient

the gradual increase in temperature with depth in the crust

what happens to the ions when the temp of the liquid drops?

the ions pack more closely together as their rate of movement slows -when cooled sufficiently, forces of the chemical bond will confine ions to an orderly crystalline arrangment -silicon and oxygen atoms link together (silicon oxygen tetrahedra)

melt

the liquid portion of magma excluding the solid crystals -composed mainly of mobile ions of the 8 most common elements found in earths crust (silicon and oxygen with lesser amounts of Al, K, Na, Ca, Fe, and MG

we get hydrothermal veins when

we have water cooling inside the earth

magma's solid component (if any)

the silicate minerals that have already crystallized from the melt -as magma body cools the size/# of crystals increase -during last stage of cooling, magma body="crystalline mush" with only small amounts of melt

igneous rocks are classified (or grouped) on the basis of what 2 things?

their texture and mineral composition

texture

used to describe the overall appearance of a rock based on the size, shape, and arrangement of its mineral grains

common features of many extrusive rocks are the voids left by gas bubbles that escape as lava solidifies-->nearly spherical openings called _____

vesicles

rocks that contain vesicles are said to have what texture?

vesicular texture -usually form in the upper zone of a lava flow (where cooling occurs rapidly enough to preserve the openings)

____cause rock to melt at lower temperatures

volatiles -addition of water lowers the melting temperature

the gaseous component of magma is called ______

volatiles -gases tend to separate as it moves toward the surface (low-pressure enviornment) -as gases build up->may propel magma from the vent when deeply burried magma bodies crystallize the remaining volatiles collect as hot, water-rich fluids that migrate thru the surronding rocks

extrusive igneous rocks= _____

volcanic rocks (named after the roman G-D of fire, Vulcan)

what are 3 most common volatiles found in magma?

water vapor (H20) carbon dioxide (CO2) Sulfur dioxide (S02)

how are tabular intrusive bodies produced?

when magma is forcibly injected into a fracture or zone of weakness

placer

when we find gold as deposits on the batholiths "gold nuggets"-->source of gold -deposit formed when heavy minerals are mechanically concentrated